282 research outputs found
First-principles extrapolation method for accurate CO adsorption energies on metal surfaces
We show that a simple first-principles correction based on the difference
between the singlet-triplet CO excitation energy values obtained by DFT and
high-level quantum chemistry methods yields accurate CO adsorption properties
on a variety of metal surfaces.
We demonstrate a linear relationship between the CO adsorption energy and the
CO singlet-triplet splitting, similar to the linear dependence of CO adsorption
energy on the energy of the CO 2* orbital found recently {[Kresse {\em et
al.}, Physical Review B {\bf 68}, 073401 (2003)]}. Converged DFT calculations
underestimate the CO singlet-triplet excitation energy ,
whereas coupled-cluster and CI calculations reproduce the experimental . The dependence of on is used
to extrapolate for the top, bridge and hollow sites for the
(100) and (111) surfaces of Pt, Rh, Pd and Cu to the values that correspond to
the coupled-cluster and CI value. The correction
reproduces experimental adsorption site preference for all cases and obtains
in excellent agreement with experimental results.Comment: Table sent as table1.eps. 3 figure
Performance of ALICE pixel prototypes in high energy beams
The two innermost layers of the ALICE inner tracking system are instrumented
with silicon pixel detectors. Single chip assembly prototypes of the ALICE
pixels have been tested in high energy particle beams at the CERN SPS.
Detection efficiency and spatial precision have been studied as a function of
the threshold and the track incidence angle. The experimental method, data
analysis and main results are presented.Comment: 10 pages, 9 figures, contribution to PIX2005 Workshop, Bonn
(Germany), 5-8 September 200
Beam Test Performance and Simulation of Prototypes for the ALICE Silicon Pixel Detector
The silicon pixel detector (SPD) of the ALICE experiment in preparation at
the Large Hadron Collider (LHC) at CERN is designed to provide the precise
vertex reconstruction needed for measuring heavy flavor production in heavy ion
collisions at very high energies and high multiplicity. The SPD forms the
innermost part of the Inner Tracking System (ITS) which also includes silicon
drift and silicon strip detectors. Single assembly prototypes of the ALICE SPD
have been tested at the CERN SPS using high energy proton/pion beams in 2002
and 2003. We report on the experimental determination of the spatial precision.
We also report on the first combined beam test with prototypes of the other ITS
silicon detector technologies at the CERN SPS in November 2004. The issue of
SPD simulation is briefly discussed.Comment: 4 pages, 5 figures, prepared for proceedings of 7th International
Position Sensitive Detectors Conference, Liverpool, Sept. 200
First Observation of Coherent Production in Neutrino Nucleus Interactions with 2 GeV
The MiniBooNE experiment at Fermilab has amassed the largest sample to date
of s produced in neutral current (NC) neutrino-nucleus interactions at
low energy. This paper reports a measurement of the momentum distribution of
s produced in mineral oil (CH) and the first observation of coherent
production below 2 GeV. In the forward direction, the yield of events
observed above the expectation for resonant production is attributed primarily
to coherent production off carbon, but may also include a small contribution
from diffractive production on hydrogen. Integrated over the MiniBooNE neutrino
flux, the sum of the NC coherent and diffractive modes is found to be (19.5
1.1 (stat) 2.5 (sys))% of all exclusive NC production at
MiniBooNE. These measurements are of immediate utility because they quantify an
important background to MiniBooNE's search for
oscillations.Comment: Submitted to Phys. Lett.
Constraints on Dark Matter Annihilation in Clusters of Galaxies with the Fermi Large Area Telescope
Nearby clusters and groups of galaxies are potentially bright sources of
high-energy gamma-ray emission resulting from the pair-annihilation of dark
matter particles. However, no significant gamma-ray emission has been detected
so far from clusters in the first 11 months of observations with the Fermi
Large Area Telescope. We interpret this non-detection in terms of constraints
on dark matter particle properties. In particular for leptonic annihilation
final states and particle masses greater than ~200 GeV, gamma-ray emission from
inverse Compton scattering of CMB photons is expected to dominate the dark
matter annihilation signal from clusters, and our gamma-ray limits exclude
large regions of the parameter space that would give a good fit to the recent
anomalous Pamela and Fermi-LAT electron-positron measurements. We also present
constraints on the annihilation of more standard dark matter candidates, such
as the lightest neutralino of supersymmetric models. The constraints are
particularly strong when including the fact that clusters are known to contain
substructure at least on galaxy scales, increasing the expected gamma-ray flux
by a factor of ~5 over a smooth-halo assumption. We also explore the effect of
uncertainties in cluster dark matter density profiles, finding a systematic
uncertainty in the constraints of roughly a factor of two, but similar overall
conclusions. In this work, we focus on deriving limits on dark matter models; a
more general consideration of the Fermi-LAT data on clusters and clusters as
gamma-ray sources is forthcoming.Comment: accepted to JCAP, Corresponding authors: T.E. Jeltema and S. Profumo,
minor revisions to be consistent with accepted versio
Adsorption of mono- and multivalent cat- and anions on DNA molecules
Adsorption of monovalent and multivalent cat- and anions on a deoxyribose
nucleic acid (DNA) molecule from a salt solution is investigated by computer
simulation. The ions are modelled as charged hard spheres, the DNA molecule as
a point charge pattern following the double-helical phosphate strands. The
geometrical shape of the DNA molecules is modelled on different levels ranging
from a simple cylindrical shape to structured models which include the major
and minor grooves between the phosphate strands. The densities of the ions
adsorbed on the phosphate strands, in the major and in the minor grooves are
calculated. First, we find that the adsorption pattern on the DNA surface
depends strongly on its geometrical shape: counterions adsorb preferentially
along the phosphate strands for a cylindrical model shape, but in the minor
groove for a geometrically structured model. Second, we find that an addition
of monovalent salt ions results in an increase of the charge density in the
minor groove while the total charge density of ions adsorbed in the major
groove stays unchanged. The adsorbed ion densities are highly structured along
the minor groove while they are almost smeared along the major groove.
Furthermore, for a fixed amount of added salt, the major groove cationic charge
is independent on the counterion valency. For increasing salt concentration the
major groove is neutralized while the total charge adsorbed in the minor groove
is constant. DNA overcharging is detected for multivalent salt. Simulations for
a larger ion radii, which mimic the effect of the ion hydration, indicate an
increased adsorbtion of cations in the major groove.Comment: 34 pages with 14 figure
Interaction of inflammatory cytokines and erythropoeitin in iron metabolism and erythropoiesis in anaemia of chronic disease
In chronic inflammatory conditions increased endogenous release of specific cytokines (TNFα, IL-1, IL-6, IFNγ and others) is presumed. It has been shown that those of monocyte lineage play a key role in cytokine expression and synthesis. This may be associated with changes in iron metabolism and impaired erythropoiesis and may lead to development of anaemia in patients with rheumatoid arthritis. Firstly, increased synthesis of acute phase proteins, like ferritin, during chronic inflammation is proposed as the way by which the toxic effect of iron and thereby the synthesis of free oxy-radicals causing the damage on the affected joints, may be reduced. This is associated with a shift of iron towards the mononuclear phagocyte system which may participate in the development of anaemia of chronic disease. Secondly, an inhibitory action of inflammatory cytokines (TNFα, IL-1), on proliferation and differentiation of erythroid progenitors as well as on synthesis of erythropoietin has been shown, thereby also contributing to anaemia. Finally, chronic inflammation causes multiple, complex disturbances in the delicate physiologic equilibrium of interaction between cytokines and cells (erythroid progenitors, cells of mononuclear phagocyte system and erythropoietin producing cells) leading to development of anaemia of chronic disease (Fig. 1)
HighPâTNano-Mechanics of Polycrystalline Nickel
We have conducted highPâTsynchrotron X-ray and time-of-flight neutron diffraction experiments as well as indentation measurements to study equation of state, constitutive properties, and hardness of nanocrystalline and bulk nickel. Our lattice volumeâpressure data present a clear evidence of elastic softening in nanocrystalline Ni as compared with the bulk nickel. We show that the enhanced overall compressibility of nanocrystalline Ni is a consequence of the higher compressibility of the surface shell of Ni nanocrystals, which supports the results of molecular dynamics simulation and a generalized model of a nanocrystal with expanded surface layer. The analytical methods we developed based on the peak-profile of diffraction data allow us to identify âmicro/localâ yield due to high stress concentration at the grain-to-grain contacts and âmacro/bulkâ yield due to deviatoric stress over the entire sample. The graphic approach of our strain/stress analyses can also reveal the corresponding yield strength, grain crushing/growth, work hardening/softening, and thermal relaxation under highPâTconditions, as well as the intrinsic residual/surface strains in the polycrystalline bulks. From micro-indentation measurements, we found that a low-temperature annealing (T < 0.4 Tm) hardens nanocrystalline Ni, leading to an inverse HallâPetch relationship. We explain this abnormal HallâPetch effect in terms of impurity segregation to the grain boundaries of the nanocrystalline Ni
Relations between Financing and Output in the Not-for-Profit Hospital
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68639/2/10.1177_107755878804500204.pd
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